1. Technical Field
The present invention relates generally to jigs, and more particularly to a coupling device of a jig.
2. Description of Related Art
Jigs are used to repeatedly and accurately produce great amount of products, and there are various types of jigs compatible for different processing methods and different usages. For example, a jig applied for electrical discharge machining (EDM) is usually placed in an EDM machine which is connected to a power source. A metal workpiece is engaged to a coupling device, and the coupling device is coupled with a jig to process the workpiece. Therefore, the coupling device can be conveniently decoupled from the jig with the workpiece still engaged thereto.
As shown in FIG. 1, a conventional coupling device 1 includes a foundation 10, a tube 12, a plurality of balls 14, and a piston base 16. Metal workpieces are placed on the foundation 10, wherein the foundation 10 has a chamber 102 within and a perforation 104 which communicates the chamber 102 and an exterior of the foundation 10. The tube 12 is engaged to the foundation 10, and is inserted in the perforation 104. The tube 12 has a plurality of through holes 122 for housing the balls 14. The piston base 16 is provided in the chamber 102, and movably fitted to the tube 12. The piston base 16 has an inner surface facing an outer surface of the tube, wherein the inner surface has a circular groove 162 and a smooth inclined section 164. Whereby, when the piston base 16 is moved to let the circular groove 162 correspond to the balls 14, a plug 182 of a jig 18 is able to be moved in or out the tube 12 smoothly. While the plug 182 is moved into the tube 12, a head 182a of the plug 182 pushes the balls 14 aside. After that, the piston base 16 is moved to let the inclined section 164 abut against the balls 14, and therefore the balls 14 restrict the neck 182b of the plug 182 to couple the coupling device 1 to the jig 18.
As shown in FIG. 2, the inclined section 164 abuts against each ball 14 with a single point. When the coupling device 1 is applied with a shear force, these single points are the only bearers for the force. As a result, the surface of the inclined section 164 tends to dent, which leads to slight mismatch between the coupling device 1 and the jig 18, and thus affects the processing accuracy of the workpieces.